The Effects of Sargassum thunbergii on the Growth of Sea Cucumbers and the Water Environment

Abstract:

To determine the appropriate farming capacity and the density of sea cucumbers and Sargassum thunbergii in certain volume of water, we analyzed the growth of sea cucumbers and S. thunbergii and the changes in the condition of the water from April to May, 2014. The results showed that the mean daily weight gain rate (Mdwg) and the specific growth rate (SGR) of sea cucumbers and S. thunbergii were significantly affected by their densities (P<0.05). In the absence of S. thunbergii, sea cucumbers showed poor growth performance when the density was 750, 500 and 250 g/m3. The growth was much improved when the sea cucumber density was 250 g/m3 and the S. thunbergii density was 1000 g/m3 and 1500 g/m3 respectively. The highest SGR of S. thunbergii appeared when the densities of sea cucumbers and S. thunbergii were 750 g/m3 and 500 g/m3 respectively, and the lowest SGR of S. thunbergii appeared when the densities of sea cucumber and S. thunbergii were 250 g/m3 and 1500 g/m3 respectively. The levels of NH4+-N, NO3–-N, NO2–-N and PO4–-P were significantly affected by the density of sea cucumbers and S. thunbergii (P<0.05). The levels of NH4+-N, NO3–-N, NO2–-N and PO4–-P in the experimental group was relatively high when the sea cucumber densities were 750, 500 and 250 g/m3, and reached the highest when the density was 750 g/m3. The levels of NH4+-N, NO3–-N, NO2–-N and PO4–-P in the experimental group were relatively low when the sea cucumber density was 250 g/m3 and the S. thunbergii density was 1000 g/m3 and 1500 g/m3. In conclusion, the growth of sea cucumbers was significantly affected by the density of S. thunbergii, and S. thunbergii had high absorption capacity to the trophic factors in water. Under the experimental conditions, the appropriate density of sea cucumbers should be 250 g/m3 and the density of S. thunbergii should be 1000 g/m3 or 1500 g/m3.